1. Field of the Invention
The present invention generally relates to an inverter circuit and a control circuit thereof and, more particularly, to an inverter circuit and its associated control circuit for converting DC power from the renewable energy or distributed energy into AC power so as to be fed into the AC utility power system according to related regulations.
2. Description of the Prior Art
With the development towards industrialization, the demand for electricity increases. However, the limited natural resources and the resistance of building new power plants due to the rise in environmental consciousness encourage developing the renewable energy. It has attracted considerable attention in efficiently and economically converting the renewable energy to the AC utility power system for developed countries to look after both industrialization and environmental protection.
The grid-tied power conditioner directly converts power from the renewable energy or distributed energy into AC power so as to be fed into the AC utility power system. The grid-tied power conditioner can be used as a stand-alone compact power generator so as to construct a distributed power system without a large-volume, high-cost and hard-to-maintain battery set. With the use of a net meter, the subscriber, possibly forming a residential power generating system, can even charge the power service provider. In this manner, the power generating cost can be relatively lowered so as to improve the efficiency.
The cost for power generating by using the renewable energy or distributed energy depends on the power generating techniques. Therefore, the utilization rate of the renewable energy or distributed energy can be increased if the power conversion efficiency can be improved.
Please refer to FIG. 1, which is a conventional two-stage inverter circuit. The inverter circuit comprises a buck-boost converter 11 and a DC-to-AC inverter 12 having two half-bridge inverters. The buck-boost converter 11 converts the input DC voltage with different voltage values to a fixed output DC voltage. The DC-to-AC inverter 12 converts the output DC voltage to an AC voltage. More particularly, the buck-boost converter 11 comprises an active switch G11, a coupled inductor L11 comprising two windings using a common iron core so that the coupled inductor L11 can be an energy storage device, two passive switches D11, D12, and three capacitors C11, C12, C13.connected to the coupled inductor and the DC-to-AC inverter. The DC-to-AC inverter 12 comprises two half-bridge inverters, each has two active switches G12, G13 (or G14, G15), two inductors L12, L13 and two capacitors C14, C15. The active switch G11 is turned on so that the energy from the DC voltage V11 is stored in the coupled inductor L11. Since the coupled inductor L11 has two windings using a common iron core, the energy is coupled by the iron core so that the buck-boost inverter 11 outputs two DC voltages V12, V13, each to be converted to an AC voltage by one of the two half-bridge inverters.
In order to improve the efficiency of the inverter circuit, the present invention provides an inverter circuit and a control circuit of the inverter circuit to prevent the switching loss of the active switch and the energy loss of the coupled inductor by use of a by-pass passive switch and improve the efficiency of the inverter circuit by use of voltage feed-forward compensation.